I'd say one should judge by other symptoms: what emotions does the patient experience and how do they behave. If the patient is depressed, apathetic and/or pers

I'd say one should judge by other symptoms: what emotions does the patient experience and how do they behave. If the patient is depressed, apathetic and/or persistently euphoric, walks naked in the middle of a city, ignores his chores or attacks people "because they are illusory and the hand isn't even mine so why not" that's an illness. If he behaves like an reasonable compassionate person and seems happy that's good - a reasonable degree of dissociation can actually make a person better, happier and more stable mentally. Simplifying I'd conclude that this is not a binary but an spectral phenomenon: there are 2, both undesirable, poles of extremity and a harmonious middle. Naturally/culturally people are more inclined to self-association and a slight shift to the opposite generally is desirable. Dissociate from your mind but don't in a degree when you loose it.